"Why did the prime minister ever think that the gentleman in question was fit and proper to be the Speaker of our country?" Mr Abbott told reporters in Brisbane on Tuesday.

Mr Abbott said it was up to Mr Slipper to decide if he should resign from the parliament.

The member for the Sunshine Coast seat of Fisher will appear in Canberra Magistrates Court on February 15 where he will be formally charged.

It is understood the charges have nothing to do with an issue relating to the use of blank taxi dockets raised, and later dropped, in a civil court matter brought by Mr Slipper's former staffer James Ashby.

The charges are believed to relate to Mr Slipper's use of hire cars in January, March and June 2010, when he was a Liberal National Party MP.

It is alleged he used the cars beyond the boundary of the ACT - breaching a little-known rule concerning MPs' travel.